In a submarine cable system, there is known a configuration, in which when a failure has occurred in any of power feed lines for supplying constant direct current to a repeater or to a branching device, a power feed line is switched (power feed lines are re-configured) in order to reduce the area affected by the failure (see e.g. Patent Literature 1 [PTL 1]).
The submarine cable system described in PTL 1 is such that, as illustrated in FIG. 7, repeaters 74 to 76 are disposed between a branching device 70, and each of terminal stations 71 to 73. Further, the branching device 70, and the terminal station devices 71 to 73 are connected by paths 77 to 79 constituting power feed lines, and optical fibers 80 to 82, respectively. In a state that a failure has not occurred in the paths 77 to 79, the path 77 and the path 78 are connected by a power feed line contact circuit (not illustrated) in the branching device 70, and the path 79 and the sea ground are connected. Electric power is supplied to the repeaters 74 and 75 by allowing constant direct current to flow from the terminal station 71 (+) to the terminal station 72 (−) via the paths 77 and 78, and electric power is supplied to the repeater 76 by allowing constant direct current to flow from the sea ground (+) to the terminal station 73 (−) via the path 79.
Next, an operation to be performed when a failure has occurred in a power feed line is explained. For instance, it is assumed that a failure has occurred in the path 78 between the branching device 70 and the terminal station 72.
When a failure has occurred in the path 78, one of the terminal stations 71 to 73 transmits, to the branching device 70, a control signal for switching a power feed line by superimposing the control signal on a signal to be transmitted via the optical fibers 80 to 82. Then, a control unit (not illustrated) in the branching device 70 controls the power feed line contact circuit in accordance with the superimposed control signal for switching the power feed line. Specifically, the path 77 and the path 79 are connected, and the path 78 and the sea ground are connected. In this state, constant direct current is allowed to flow from the terminal station 71 (+) to the terminal station 73 (−) via the paths 77 and 79, whereby electric power is supplied to the repeaters 74 and 76.
Further, in PTL 1, the branching device is provided with a monitoring means which monitors an electrical potential of a switch for switching a power feed line at a branching point, and a monitor signal output means which outputs the electrical potential monitored by the monitoring means to a terminal station via an optical fiber. The terminal station connected to the power feed line is configured such that the power feed line is switched at the branching point by a control signal, while monitoring the electrical potential of the switch at the branching point, which is received through the optical fiber for switching the power feed line. Thus, electrical stress on the switch for switching a power feed line is reduced.